In the standards organization 3GPP (3rd Generation Partnership Project), studies are conducted for 3GPP LTE (Long Term Evolution) to realize further improvement of present third mobile phone systems. An OFDM scheme is likely to be adopted as a downlink radio communication scheme disclosed in Non-patent Document 1 that fulfills the requirements of the LTE system.
In cellular systems such as the mobile phone systems, cell search technique of searching for the optimal base station to connect the radio link by mobile stations upon starting communication, upon performing a handover, upon waiting communication for carrying out intermittent reception, and so on, is one of significant functions. In the standardization meetings, various cell search methods in LTE systems are studied (see Non-Patent Document 2).
FIG. 1 shows the configuration of synchronization channel (SCH) proposed in Non-Patent Document 2. As shown in the figure, in a ten millisecond radio frame, SCHs are multiplexed on the tail symbols in the tenth and twelfth subframes in the frequency domain. The bandwidth where the SCHs are allocated is placed in the central 1.25 MHz in the bandwidth assigned to the base station. Further, SCHs are classified into two kinds, that is, primary SCHs (P-SCHs) and secondary SCHs (S-SCHs).
In the first step of cell search processing in this cell search method, the receiver performs correlation detection between a received signal and a P-SCH replica signal the receiver holds, to detect the symbol timing. Here, averaging the correlation outputs of P-SCHs at two positions in one radio frame allows symbol timing detection characteristics to improve. In the second step, the receiver performs a DFT on a received signal at the symbol timing acquired in the first step and performs correlation detection with respect to the S-SCHs in the frequency domain, to detect the frame timing and the cell ID group. In the third step, the receiver acquires the correlation with respect to the reference signal multiplied by the scrambling code unique to the cell belonging to the detected cell ID group and detects a cell ID from the detected group.    Non-patent Document 1: 3GPP, TR 25.913v7.0.0 (2005-06), “Requirements for Evolved UTRA and UTRAN”    Non-patent Document 2: 3GPP, R1-061187, NTT DoCoMo, Fujitsu, Mitsubishi Electric, NEC, Panasonic, Toshiba Corporation “Comparison on Cell Search Time Performance between SCH-Replica Based and Auto-Correlation Based Detections in E-UTRA Downlink”